Cantilever piezoelectric energy harvesting from ambient vibrations is a viable solution for powering wireless sensors and low-power electronics. However, the greatest issue preventing these systems from being widely used is their poor reliability. With the aim to maximise their power output, the devices are often operated close the fracture strength, which results in cracks in the brittle piezoceramic layer. Tapered cantilevers are suggested to improve the mechanical reliability. A relative comparison is made between tapered piezoelectric cantilevers and conventional rectangular cantilevers in terms of reliability and power output. Tensional strains causing fractures show a serious reduction of power output and eigenfrequency. Experiments show that tapered cantilevers have a higher power output per unit area.